Degli Esposti Mauro
Cancer Research Campaign Molecular Pharmacology Group, School of Biological Sciences, Stopford Building, University of Manchester, M13 9PT, Manchester, UK.
Biochim Biophys Acta. 2002 Feb 15;1553(3):331-40. doi: 10.1016/s0005-2728(02)00187-1.
Pro-apoptotic proteins of the Bcl-2 family are known to act on mitochondria and facilitate the release of cytochrome c, but the biochemical mechanism of this action is unknown. Association with mitochondrial membranes is likely to be important in determining the capacity of releasing cytochrome c. The present work provides new evidence suggesting that some pro-apoptotic proteins like Bid have an intrinsic capacity of binding and exchanging membrane lipids. Detailed analysis indicates a significant sequence similarity between a subset of Bcl-2 family proteins including Bid and Nix and plant lipid transfer proteins. The similar structural signatures could be related to common interactions with membrane lipids. Indeed, isolated Bid shows a lipid transfer activity that is even higher than that of plant lipid transfer proteins. To investigate the possible relevance of these structure-function correlations to the apoptotic action of Bid, cell free assays were established with isolated mitochondria, recombinant Bid and a variety of exogenous lipids. Micromolar concentrations of lysolipids such as lysophosphatidylcholine were found to change the association of Bid with mitochondria and also stimulate the release of cytochrome c promoted by Bid. The changes in mitochondrial association and cytochrome c release were enhanced by the presence of liposomes of lipid composition similar to that of mitochondrial membranes. Thus, a mixture of liposomes, mitochondria and key lysolipids could reproduce the conditions enabling Bid to transfer lipids between donor and acceptor membranes, and also change its reversible association with mitochondria. Bid was also found to enhance the incorporation of a fluorescent lysolipid, but not of a related fatty acid, into mitochondria. On the basis of the results presented here, it is hypothesised that Bid action may depend upon its capacity of exchanging lipids and lysolipids with mitochondrial membranes. The hypothesis is discussed in relation to current models for the integrated action of pro-apoptotic proteins of the Bcl-2 family.
已知Bcl-2家族的促凋亡蛋白作用于线粒体并促进细胞色素c的释放，但其作用的生化机制尚不清楚。与线粒体膜的结合可能对决定释放细胞色素c的能力很重要。目前的研究提供了新的证据，表明一些促凋亡蛋白如Bid具有结合和交换膜脂的内在能力。详细分析表明，包括Bid和Nix在内的一部分Bcl-2家族蛋白与植物脂转移蛋白之间存在显著的序列相似性。相似的结构特征可能与与膜脂的共同相互作用有关。事实上，分离出的Bid显示出比植物脂转移蛋白更高的脂转移活性。为了研究这些结构-功能相关性与Bid凋亡作用的可能关联，利用分离的线粒体、重组Bid和多种外源脂质建立了无细胞分析方法。发现微摩尔浓度的溶血磷脂如溶血磷脂酰胆碱会改变Bid与线粒体的结合，并刺激Bid促进的细胞色素c的释放。脂质组成与线粒体膜相似的脂质体的存在增强了线粒体结合和细胞色素c释放的变化。因此，脂质体、线粒体和关键溶血磷脂的混合物可以重现使Bid在供体膜和受体膜之间转移脂质并改变其与线粒体可逆结合的条件。还发现Bid增强了一种荧光溶血磷脂而非相关脂肪酸进入线粒体的过程。基于此处给出的结果，推测Bid的作用可能取决于其与线粒体膜交换脂质和溶血磷脂的能力。结合目前关于Bcl-2家族促凋亡蛋白综合作用的模型对该推测进行了讨论。
